The use of an inflatable tourniquet cuff to occlude blood flow into a subject's limb, thereby providing a bloodless surgical field in the portion of the limb distal to the cuff over a period of time suitably long for the performance of a surgical procedure, is well known in surgical practice. Tourniquet systems typically include an inflatable cuff for encircling a limb at a selected location and a tourniquet instrument for maintaining the pressure in the cuff near a selected pressure. Such tourniquet instruments of the prior art typically contain, or connect to, a source of pressurized gas and include a pressure regulating mechanism for controlling and maintaining the pressure of the gas supplied to the tourniquet cuff near the selected pressure.
Typically a variety of cuff sizes are provided so that a cuff that overlaps itself when encircling the limb may be selected, thereby ensuring that pressure is applied to the limb around its entire circumference. Cuffs are also provided in a variety of shapes, widths, materials, configurations and other physical characteristics as required for different types of patients, limb locations, and surgical procedures.
Other physical characteristics of the cuff may be the manufacturer of the cuff, the state of sterility or non-sterility of the cuff as supplied by the manufacturer, the size, shape and potential volume of the inflatable bladder or chamber within the cuff, the number of uses the cuff is designed for, and any physical changes that may have resulted from surgical use and any reprocessing after use.
Other physical characteristics of the cuff may be the manufacturer of the cuff, the state of sterility or non-sterility of the cuff as supplied by the manufacturer, the size, shape and potential volume of the inflatable bladder or chamber within the cuff, the number of uses the cuff is designed for, and any physical changes that may have resulted from surgical use and any reprocessing after use.
Modern tourniquet instruments of the prior art employ digital electronic technology in the regulation of pressure for the tourniquet cuff and in the detection of certain hazardous conditions. However the pressure selected at the tourniquet instrument for regulation within the tourniquet cuff has often been very arbitrarily chosen by surgical staff, regardless of the type or size of cuff connected to the tourniquet instrument. More recently, some surgical staff are selecting lower tourniquet pressures based on the surgeon's estimate of the minimum pressure required to safely occlude blood flow past the cuff in a specific patient. This minimum safe pressure is affected by a number of variables, including the physical characteristics of the specific tourniquet cuff attached to the patient, and so providing a convenient, reliable and automatic means for the tourniquet instrument to identify certain physical characteristics of that cuff (such as length, width, and type) is useful for adapting the estimate of the minimum safe pressure, either manually with the involvement of the surgical staff or automatically by the tourniquet instrument connected to the cuff. For example, if a wide cuff is identified as being connected to the tourniquet instrument, then the instrument may display instructions to the surgeon to select a lower tourniquet pressure setting than the arbitrary pressure setting that might otherwise be used, to reduce the likelihood of pressure related injury while still stopping blood flow effectively, or the tourniquet instrument may automatically adapt the tourniquet pressure setting to that lower pressure.
Automatic identification of the specific cuff connected to the tourniquet instrument also allows adaptation of the settings of important operating and safety parameters of the tourniquet instrument and system as a whole. For example, if a very small pediatric tourniquet cuff is automatically identified as being connected to the tourniquet instrument, then the maximum allowable tourniquet pressure setting can be adapted and reduced to a much lower and safer maximum level without affecting the efficacy of the overall system. Also, the settings of certain alarm parameters within the instrument may be adapted upon automatic identification of the cuff connected to the instrument; for example, the maximum time limits allowed within the instrument for cuff inflation and for cuff deflation may be automatically adapted as a function of the size of the inflatable portion of the connected cuff, to provide a safety alarm signal in the event of a hazardous inability of the instrument to inflate or deflate the cuff within a normal maximum time period while also preventing the generation of false alarm signals.
Upon automatic identification of the specific size and type of cuff connected to the tourniquet instrument, and thus the size, shape and potential volume of the inflatable portion of the connected cuff, the settings of other parameters important in the regulation of tourniquet pressure can be adapted to improve the accuracy and responsiveness of pressure regulation. Further, if the cuff type can be automatically identified by a connected tourniquet instrument, then cuff-related data needed for a surgical record may be automatically generated and kept more easily and more accurately for inventory control and cuff utilization purposes. Such a record may also be used (in combination with recording of other parameters such as pressure used) to aid in establishing safer practice guidelines for the use of surgical tourniquets.
Cuffs and tourniquet instruments are made by various manufacturers, and it is presently possible for users to connect a tourniquet instrument made by one manufacturer to tourniquet cuffs made by other, unknown manufacturers. However, at least one tourniquet instrument known in the prior art has advanced safety and performance features that are specifically designed to work with tourniquet cuffs that are made by the same manufacturer (see, for example McEwen in U.S. Pat. No. 5,649,954 and McEwen in U.S. Pat. No. 5,681,339). Such safety features and operational features in a tourniquet instrument may not function, or may not function predictably or properly if a cuff from an unknown manufacturer is connected to the tourniquet instrument. Therefore, to avoid or minimize safety hazards, and to minimize potential legal liability for users and for the manufacturer of the tourniquet instrument, it is useful to have a tourniquet instrument that has the capability to automatically identify the manufacturer of the connected cuff and to accordingly adapt the settings of important safety parameters, operating parameters and messages and warnings to users. For example, if such an instrument detects that an unknown cuff type is connected, the instrument could display a warning to the user that certain important functions relating to safety and performance may be disabled. Also, a tourniquet system having the capability to automatically identify the type of connected cuff can permit the sale or lease of the instrument to a user on a peruse basis or in connection with the purchase of specified quantities of cuffs of a known and identifiable type. A variety of related functions could also be performed by a tourniquet instrument having the capability to automatically identify that connected cuffs were, or were not, made by a known manufacturer. For example if an unidentifiable cuff from an unknown manufacturer were connected to such an instrument, the instrument could be programmed to be non-operational; alternatively, the tourniquet instrument could be programmed to remain as operational as possible but warn of the use of an unidentifiable cuff and record the event, so as not to prevent or delay needed surgery.
Many tourniquet cuffs are designed for to be reused in multiple surgical procedures and are supplied by the manufacturer in a non-sterile state. Other tourniquet cuffs are designed for single use only, and are supplied in a sterile state (eg. ‘Comforter™ Disposable Gel Cuff’ sold by DePuy Orthopaedics Inc., ‘Zimmer ATS Disposable Tourniquet Cuffs’, Zimmer Patient Care, Dover, Ohio). These cuffs are used when sterility is required in the area where the cuff is applied, and when the cuff must not be re-used in order to prevent cross-contamination between patients. Such single-use sterile cuffs are designed to withstand a specified sterilization process (conducted by the manufacturer) and the typical stresses encountered in a single surgical procedure. Subsequent sterilization or processing may lead to hazardous conditions such as compromised sterility, deteriorated physical condition and possibly sudden failure of the cuff during surgery. In particular, exposure to high temperatures or ethylene oxide gas during sterilization can degrade the materials in these cuffs. Despite these risks, it is increasingly common for users to attempt to reprocess and re-use single-use sterile cuffs using cleaning processes that have not been approved or tested by the original manufacturer. For example, single-use sterile cuffs are routinely reprocessed by at least one company that uses a pasteurization process (which subjects the cuff to high temperature and humidity), and then returned to the user in a ‘high-level disinfected’ state, a non-sterile, lower state of cleanliness than when originally supplied by the manufacturer. Several other companies routinely reprocess single-use sterile tourniquet cuffs using ethylene oxide gas sterilization methods, returning the cuff in a surgically sterile state. Other sterilization methods (such as gamma or electron beam radiation and gas plasma processes) could conceivably be used to reprocess cuffs; however ethylene oxide gas is currently the most common and practical method due to availability of facilities and its suitability for small batch sizes. If exposure to such attempts to reprocess and re-sterilize sterile cuffs after surgical use could be automatically identified by the tourniquet instrument, the tourniquet instrument could adapt by activating various warning functions to alert the user and reduce potential hazards to the patient. No tourniquet cuff is known in the prior art that allows a tourniquet instrument to identify whether a connected cuff has been subjected to a subsequent re-sterilization process, and to adapt its operation accordingly.
Many prior-art tourniquet cuffs are color-coded to indicate size to a user by visual inspection. For example the ‘Comforter™ Disposable Gel Cuff’ sold by DePuy Orthopaedics Inc. has a color dot on the outer packaging label corresponding to the cuff size, but no indication of cuff size on the cuff itself. In several other types of tourniquet cuff (for example ‘Zimmer ATS Disposable Tourniquet Cuffs’, Zimmer Patient Care, Dover, Ohio), components permanently attached to the cuff (such as edge trim and/or tie ribbon) are made of a selected color of material corresponding to the cuff size. These identification means are solely visual and interpretable by the user who is familiar with the color coding scheme. No communication with a tourniquet instrument is automatically established by connection of the cuff to the instrument, and therefore the instrument necessarily cannot automatically adapt the settings of important parameters of operation and safety in response to the size and type of cuff connected to the instrument.
In U.S. Pat. No. 4,605,010, McEwen describes a tourniquet cuff that includes an electrical means for identifying remotely the physical characteristics of the cuff, as well as for remotely determining the circumference of the limb encircled by the cuff. To permit remote identification of cuff type, the McEwen '010 cuff includes electrically conductive components within the cuff structure, and requires an electrical connection as well as a pneumatic connection between the tourniquet cuff and the tourniquet instrument. Thus electrical power and an electrically conductive pathway are necessarily present within the cuff, in close proximity to the patient's limb encircled by the cuff. This can present a hazard to the patient under some circumstances. Also, inclusion of electrical components within the tourniquet cuff significantly increases the cost and complexity of manufacture of such cuffs, and their reliability at time of manufacture and subsequently during use. The prior art tourniquet cuff described by McEwen '010 includes means for allowing a connected tourniquet instrument to remotely determine the circumference of the limb encircled by the cuff. This permits the tourniquet pressure setting to be adjusted, based on the relationship between the physical characteristics of the remotely identified cuff and the remotely identified circumference of the limb encircled by the cuff. No other tourniquet systems in the prior art known to the inventors of the current invention establish a connection other than a pneumatic connection between the cuff and the instrument, such that information about the cuff can be received by the instrument and such that the settings of important safety and operating parameters of the instrument can be adapted in response. Further, fundamental problems inherent in the significantly increased cost and complexity, and in the inherently decreased reliability, of the apparatus described in McEwen '010, have prevented the commercial realization of any tourniquet systems incorporating apparatus such as described in McEwen '010.
No adaptive tourniquet cuff system is known in the prior art that includes provision for the tourniquet instrument to automatically identify physical characteristics of the connected tourniquet cuff and to adapt the settings of certain safety and operating parameters in response.